Abstract: A liquefaction unit that may include a first treating unit, a second treating unit, a liquefaction heat exchanger, a changeover unit, a liquid nitrogen tank, an LNG product storage tank, and a pressure build unit. During a first operating phase, the associated piping defines a first operating phase flow path for natural gas from the natural gas inlet stream to the first treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the second treating unit. During a second operating phase, the associated piping defines a second operating phase flow path for natural gas from the natural gas inlet stream to the second treating unit to the liquefaction unit to the LNG product stream, and a first operating phase flow path for nitrogen from the liquid nitrogen stream to the liquefaction unit to the first treating unit.